1. Field of the Invention
This invention relates to the separation and classification of electrically conductive materials and to an apparatus and method for utilizing the principle of electrically induced eddy current repulsion as the means for accomplishing the separation of material. The invention is of particular importance in the separation of non-ferrous metallic articles from a mixture of non-ferrous metallics, ferrous metallics and non-metallics. For example, the invention is useful for the recovery of metal articles from municipal solid waste material.
2. Description of the Prior Art
In numerous situations, it is desirable to be able to separate materials according to their electrical conductivity, such as to separate metallic materials from non-metallic materials or to separate and distinguish between different metallic substances. The use of electromagnetically induced eddy currents to produce repulsive forces between an electromagnet and the material in which the eddy current is induced is one method for accomplishing such separation of materials. A rapid change in current through an inductor will produce a magnetic field the flux of which will be cut by any material lying within the resulting magnetic field. Since the flux varies with time and any conductive material within the field cannot link such a time varying flux, current is induced in the conductive material such as to produce a zero net flux passing through the material. This latter current, termed an eddy current, has a magnetic field associated with it, which magnetic field exerts a repelling force on the first magnetic field. Therefore, if the electromagnet is fixed in position and the other material is free to move, the material in which the eddy current has been induced will be repelled from the magnet. The repulsive force will vary directly with the value of the eddy current which will, in turn, depend upon, among other things, the electrical conductivity of the material.
In one embodiment of the electromagnetic eddy current materials separator, a mixture of particles of material with various electrical conductivity characteristics and magnetic properties may be projected through an intense unidirectional magnetic field with the line of motion of the particles essentially at 90.degree. to the direction of the field and, in accordance with the above-mentioned principles, particles of greater conductivity will be decelerated to a greater extent than those of lesser conductivity, with the result that different kinds of particles will have different trajectories in emerging from the magnetic field, and separation of the particles will thereby be achieved. It will be understood that the effect on the conducting particles will be the same whether the particles move with respect to the field or whether the field moves with respect to the particles.
The aforementioned principles are well-known and have previously been employed for the purposes of separating and classifying materials. Prior apparatus and methods for adapting the principle of electromagnetic eddy current repulsion to the separation and classification of materials have been extremely inefficient in their use of energy, have suffered from blockage of the apparatus due to the presence of ferrous materials, and have achieved a poor degree of separation because of the scattering influence of the fringe fields of the electromagnet.
The most relevant example of a prior art system known to us is that disclosed in U.S. Pat. No. 3,448,857 to Benson et al. The Benson et al patent illustrates these disadvantages, as will become more apparent from the description of our invention which follows.
It is, accordingly, an object of the invention to provide and improved electromagnetic eddy current materials separator apparatus and method.
It is a further object of the invention to provide an electromagnetic eddy current materials separator apparatus and method which is highly efficient energy-wise and economical to operate.
It is a further object of the invention to provide an electromagnetic eddy current materials separator apparatus and method capable of efficient, economical and blockage-free operation with feedback containing ferrous metals.
It is another object of the invention to provide an improved electromagnetic eddy current materials separator capable of providing a more effective separation of materials based upon their electrical conductivities.
Another object of the invention is to provide a blockage-free feed system for supplying materials, including ferrous materials, to the electromagnet of an electromagnetic eddy current materials separator.